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Cancer Disparities Not Simply Black and White

MIAMI—Years of research on the disparity in cancer mortality and morbidity between blacks and whites have done little to narrow the gap: “We're doing the same thing every year and getting the same results,” said Folakemi Odedina, PhD, Director of Community Outreach and Minority Affairs for the University of Florida's Prostate Disease Center. “Everyone seems to think black is black.”

Dr. Odedina spoke here at the American Association for Cancer Research's “Science of Cancer Health Disparities” conference, focusing on racial/ethnic minorities and the medically underserved.

Other conference speakers echoed that frustration, yet many also offered a hint of hope. They see progress in the growing realization of the diversities among groups such as African Americans that studies in the past typically included all together as one racial group.

Historically, researchers classified subjects according to their self-identified race and ethnicity (SIRE). SIRE data still has value, especially in studies of cultural and environmental influences on disparity. But it tells little about subjects' genetics. This is especially true of African Americans, who are much more genetically diverse than Americans of European descent are.

Another speaker, Stephen Freedland, MD, Associate Professor of Surgery and Pathology at Duke University, noted that it has long been known that many types of cancer have higher mortality and morbidity in African Americans. For example, black American men are 66% more likely to be diagnosed with prostate cancer than white men are and twice as likely to die of the disease, and African American women have higher rates of breast cancer and more aggressive triple-negative tumors than whites do. Colorectal cancer also strikes African Americans more than any other ethnic group.

Timothy R. Rebbeck, PhD, Professor of Epidemiology at the University of Pennsylvania School of Medicine, said that recent genetic research suggests that not all people who call themselves African American face an equal risk, and that studies have associated a higher risk for some cancers including prostate and breast with African ancestry. The greater someone's African ancestry, the higher the risk for prostate cancer, he said. “Data shows that about 20 percent of [self-identified African Americans'] genomic ancestry is non-African. Some people who have as little as five to 10 percent African ancestry call themselves African Americans.”

Genetic testing gives researchers an opportunity to separate blacks with strong African ancestry from those without. The cost per subject for genetic testing ranges from less than $100 to as much as $2,000, depending on the number of markers being examined, Dr. Rebbeck said.

“The concept of genomic ancestry is relatively new. It's becoming more and more prevalent. In the future, we hope to focus more and more on African Americans and use genetic markers.”

Still genetic testing can't explain all racial disparities in cancer, Dr. Odedina said, citing a study she conducted showing that black Nigerians who immigrated to the United States had a lower rate of prostate cancer than native African Americans, the opposite of what genetics would predict—“There was a significant difference between foreign-born and native-born.”

Another speaker, Nathan A. Ellis, MD, Associate Professor of Gastroenterology at the University of Illinois at Chicago, said that in South Africa, white men have 10 times the rate of prostate cancer compared with blacks and that such findings serve as reminders that risk is not only a product of genetics, but also of diet, environmental exposures, socioeconomic status, and access to care.

Dr. Odedina said she attributes the disparity between Nigerian immigrants and American-born blacks to diet. African Americans eat a lot more red meat and fewer vegetables than African immigrants do; and in South Africa, the opposite is true, with whites consuming more meat.

In studies of the effects of diet, poverty and culture, SIRE is a better indicator of race than genetic ancestry, Dr. Rebbeck said. “I think of SIRE as a social construct. I don't think of it as a biological construct.”

Poverty is another social factor beyond genetics that clearly influences cancer mortality.

“Poor whites have higher mortality than richer whites or blacks, but blacks on Medicaid still have higher mortality than whites on Medicaid,” Dr. Ellis said.

Complex

Because disparities are shaped by a complex mix of genetics and lifestyle factors, researchers caution colleagues against making faulty assumptions.

“We must use race when we are conducting cancer-disparities research, but with caution,” said Vence Bonham, Jr., an attorney and associate investigator with the National Human Genome Research Institute. “There's a potential for misuse or misinterpretation.”

He advised researchers at the conference to define race in their studies, report on how they use race, and include its limitations.

Eventually, genetic markers will be used to assess people's individual cancer risk, Dr. Ellis predicted. “We'll identify people with certain risk profiles, based on their individual genotype.”

If everyone has equal access to testing, that could reduce racial and ethnic disparities, but otherwise it could widen the gap. “Sometimes disparities get worse when new technology comes along, but if genomics is applied equally, things should get better.”